Step 1: Assume capitals according to the given ratio.
Let
\[
A=5x,\qquad B=3x
\]
Both invest for 12 months.
\[
A=5x\times12=60x
\]
\[
B=3x\times12=36x
\]
Step 2: Calculate C's capital-time product.
C joins after 6 months and invests equal to A.
\[
C=5x
\]
Investment duration:
\[
6 \text{ months}
\]
Thus,
\[
5x\times6=30x
\]
Step 3: Find profit ratio.
\[
60x:36x:30x
\]
\[
=10:6:5
\]
Hence,
\[
\boxed{10:6:5}
\]